Valving mechanism for hydraulic storage means, especially for hydraulic testing apparatus

ABSTRACT

The present valving mechanism forms part of the load piston cylinder means, for example, of a hydraulic testing apparatus. The load cylinder is provided with a first control inlet at each end thereof and a second control inlet substantially at each end of the resonant stroke of the piston. Storage means are connected to the load cylinder also substantially at each end of said resonant stroke. Further, control ring pistons are slideably arranged on the piston rod on each side of a piston which is fixed to the rod. The control ring pistons close or open the ports to said storage means.

United States Patent 1 Kreiskorte [75] Inventor: Heinz Kreiskorte, PostDortmundl-loerder, Germany [73] Assignee: Carl Schenck MasehinenlabrikGmhl-l, Darmstadt, Germany [22] Filed: Dec. 8, 1971 [21] Appl. No.:205,957

[30] Foreign Application Priority Data [56] References Cited UNITEDSTATES PATENTS 2,415,783 2/1947 Bassett et al ..92/65 X 1 May 8, 19732,506,374 5/1950 McMahon ..92/65 X 2,806,449 9/1957 Simmons ..91/411 A X3,312,146 4/1967 Quere et al. ..92/65 X FOREIGN PATENTS OR APPLICATIONS2,023,268 11/1970 Germany ..91/167 Primary ExaminerMartin P. SchwadronAssistant Examiner-Allen M. Ostrager Attorney-Wolfgang G. Fasse [5 7]ABSTRACT The present valving mechanism forms part of the load pistoncylinder means, for example, of a hydraulic testing apparatus. The loadcylinder is provided with a first control inlet at each end thereof anda second control inlet substantially at each end of the resonant strokeof the piston. Storage means are connected to the load cylinder alsosubstantially at each end of said resonant stroke. Further, control ringpistons are slideably arranged on the piston rod on each side of apiston which is fixed to the rod. The control ring pistons close or openthe ports to said storage means.

6 Claims, 2 Drawing Figures MUVEMENT SENSOR WEIGHTS ./4

PATENTEI] HAY 81975 SHEET 1 UF 2 MOVEMENT SENSOR WEIGHTS FIG! PATENTEU W75 SHEET 2 BF 2 MOVEMENT SENSOR CONTR L UN T S T H m E W FIGZ VALVINGMECHANISM FOR HYDRAULIC STORAGE MEANS, ESPECIALLY FOR HYDRAULIC TESTINGAPPARATUS BACKGROUND OF THE INVENTION The present invention relates to avalving mechanism for hydraulic storage means, especially for hydraulictesting apparatus. Such machines include a first hydraulic pistoncylinder arrangement for producing a dynamic, varying load preferably atthe resonance frequency of the apparatus or system, and a second pistoncylinder arrangement for producing an initial load on which the dynamicvarying load is superimposed. The two cylinder piston arrangements mayalso be operated to produce a testing load conforming to a predeterminedload characteristic. The latter mode of operation may also be referredto as a so called slow speed drive.

These hydraulic testing machines or systems are adapted for a switchover between the so called resonance operation and the so called slowspeed drive as mentioned above. The two hydraulic cylinders areconnected to the means which receive or hold the probe which is to betested mechanically. One of the cylinders produces the dynamicallyvarying load during the so called resonance operation. The othercylinder serves for producing a so called initial load upon which thereis superimposed the oscillating load produced by the resonance cylinder.In this manner, for example, it is possible to convert a pureosciilating load into a pulsating load. In this type of operation, thepiston of the second hydraulic cylinder piston arrangement, the socalled initial load piston cylinder arrangement, is subjected to loadson both of its surfaces and thus it follows the oscillating movementsproduced by the first or resonant piston cylinder arrangement. In orderto enable, the second piston to make the just-mentioned movements, it isnecessary that the pressure medium on both sides of the piston in thecylinder is connected to a respective hydraulic storage which is cableof temporarily receiving the displaced volume of pressure medium.

On the other hand, when the system is to operate in the above-mentionedslow speed drive manner, the second or initial load piston cylinderarrangement performs another function if, for example, a testing loadhaving a predetermined load characteristic is to be applied to thesample to be tested, however, without a superimposed oscillating load.In this type of operation the hydraulic storage spaces connected to eachside, that is, to the cylinder spaces above and below the second pistonwould interfere with the desired slow speed drive. Accordingly, it isnecessary to close off these storage means for the slow speed driveoperation.

The closing and opening of the conduits connecting the hydraulic storageand the cylinder of the second piston cylinder arrangement could beaccomplished by valves arranged in said conduits whereby the valves mustbe actuated either by hand or by remote control. Providing additionalvalves of course increases the costs and besides it requires a separateor additional control step from actuating these valves when the systemis to be switched for one type of operation to the other as describedabove. Anotherdisadvantage of valves in saidconduits is seen in thatthevalves act as throttle means in the conduit so that the flow of thepressure medium is dampened as it passes through these valves. Suchdampening is particularly disadvantageous because it preventsaccomplishing a large resonance rise or at least impedes the attainingof such rise.

OBJECTS OF THE INVENTION In view of the above, it is the aim of theinvention to achieve the following objects singly or in combination:

to overcome the above-outlined drawbacks, more specifically to provide avalving mechanism which is simple in construction and, so to speak,blends into the piston cylinder arrangements employed in hydraulictesting systems as described above;

to provide a valving mechanism which may be automatically operatedsimultaneously with the switching of a testing apparatus from one modeof operation to another so that no special actuating means arenecessary;

to substantially eliminate a throttling action in the conduitsconnecting a hydraulic storage means to the cylinder of a pistoncylinder arrangement, especially in a hydraulic testing system;

to assure the desired, substantial resonance rise when the machineoperates in the resonance mode, by eliminating features which impedesuch high resonance rise.

SUMMARY OF THE INVENTION According to the invention there is provided avalving mechanism for hydraulic storage means, especially for hydraulictesting systems, wherein the second cylinder which is connected to saidstorage means through respective ports in its cylinder wall and whereina piston rod which has rigidly attached thereto a piston slideable backand forth within said cylinder, is also provided with ring pistons oneof which is slideable on said piston rod on each side of saidfirst-mentioned piston. The cylinder is provided with control ports atits ends as well as substantially at .each end of the reciprocatingresonance movement of the piston, whereby upon opening of the controlports at the end of the cylinder, the ring pistons are moved to abutagainst said piston and thereby close said ports to the storage means.On the other hand, when the control ports adjacent to the end of thereciprocating resonance movement are opened, the ring pistons are movedaway from said first-mentioned piston toward the respective end of thecylinder whereby said ports to the storage means are opened.

Preferably, the ring pistons are provided with sealing means aroundtheir circumferential surface. These sealing means are preferablyarranged adjacent the end of the respective ring piston which faces awayfrom said first-mentioned piston.

BRIEF F IGURE'DESCRIPT ION In order that the invention may be clearlyunderstood, it will now be described, by way of example, with referenceto the accompanying drawings, wherein:

FIG. 1 illustrates a schematic diagram of a hydraulic testing machinewhereby the hydraulic as well as the electric circuits have beensimplified for claritys sake, said machine being capable of producing adynamic alternating load with an initial load which constitute thetesting load and wherein the arrangement is shown in the position forthe resonance mode of operation; and

FIG. 2 is a diagram similar to that of FIG. 1 but illustrating thearrangement for subjecting the test sample to static loads or to atesting load having a predetermined, slowly varying load characteristic.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS A sample 1 to be tested, forexample a tensile rod is secured at one end thereof to a load cell 2which in turn is secured to the machine frame 3 shown in simplifiedfashion. The machine frame 3 supports all the members of the hydraulictesting system. The other end of the sample 1 to be tested is secured toa mass 4 which in turn is connected to a piston rod 5. The piston rod 5has secured thereto a piston 6 which slides up and down or back andforth in a cylinder 7 which constitutes the so called means forcecylinder. The just-described piston cylinder arrangement comprising theelements 5, 6, and 7 constitutes the second piston cylinder arrangementof the system. The first piston cylinder arrangement of the systemcomprises a piston rod 9, a piston 10, and a cylinder 11. The piston rod9 and the piston rod 5 are connected to each other through anintermediate member 8. The upper end of the piston rod 9 is operativelyconnected to a movement sensing member 12.

A conventional source of hydraulic power (not shown) is connected to thefirst cylinder 11 through hydraulic conduits 13. The flow of pressuremedium through the conduits 13 is controlled by a servo-valve 14 as wellas by a hydraulic switching valve 15 in such a manner that the piston 10is alternately subjected to pressure. In other words, first one surfaceof the piston 10 is subjected to pressure to move the piston 10 and itsrod 9 in one direction and then the opposite surface of the piston 10 issubjected to pressure to move it in the opposite direction together withits piston rod and so forth. Thus, a sinusoidal, oscillating load isapplied to the sample 1 to be tested.

In order to accomplish the above sinusoidally oscillating load on thepiston 10, the servo-valve 14 is controlled by a central control unit 16in response to the movement sensor 12 and preferably through anamplifier 17 in such a manner that each of the two hydraulic conduits 13are alternately connected to the source of hydraulic pressure.

In order to superimpose an initial or mean load on the dynamic loadwhich oscillates about a zero value and which, as mentioned, is producedby the first piston cylinder arrangement 9, l0, 11, the piston 6 whichis rigidly secured to its piston rod 5 may be subjected on one of itssurfaces by hydraulic fluid either under a predetermined constantpressure or a pressure which varies relatively slowly. For this purposethe second cylinder is provided with a pair of first control ports 18located approximately at the points of return of the reciprocatingstroke of the piston 6. These control ports 18 are connected torespective hydraulic conduits for the supply and removal of hydraulicliquid. The term reciprocating stroke" designates the movement of thepiston 6 in response to the resonance movement of the piston 10. Suchreciprocating movement must be distinguished from the movement of thepiston 6 which the piston 6 performs during the so called slow motionmode of operation. The slow motion movement has a stroke which issubstantially longer than said stroke during resonance operation.

As mentioned above, FIG. 1 depicts said resonant mode of operation. Inthe position in which the control valve 19 is shown in FIG. 1, thehydraulic conduits 20 which are connected to the control ports 18 of thecylinder 7 are interconnected with further conduits 21 and through theseconduits through respective servovalves 22 and 23 to the source ofhydraulic pressure not shown. The servo-valves 22 and 23 are controlledthrough amplifiers 24 also by the control unit 16 in such a manner thatone of the two surfaces of the piston 6 is subjected to the desiredpressure.

The volume or rather the cylinder volumes adjacent to each side orsurface of the piston 6 varies very rapidly with each cycle ofoscillation because the piston 6 performs a rapid oscillatory motion inresponse to the respective oscillatory motion of the piston 10 in theresonance cylinder 11. It is not possible to open and close thehydraulic conduits 20 in an equally rapid manner. Therefore, the volumeabove the piston 6 and the volume below the piston 6 are connected torespective hydraulic storage means 26. For this purpose there areprovided connecting ports 25 which are located in the wall of thecylinder 7 about at each end of the reciprocatory movement or stroke ofthe piston 6. In other words, these connecting ports 25 are located atabout the return point of said reciprocatory movement of the piston 6.These storage means 26 receive the pressure medium volume which istemporarily displaced due to the oscillatory movements of the piston 6.

FIG. 2 is a circuit diagram illustrating the so called slow speed drive.In this mode of operation, the sample 1 to be tested is to be subjectedto static loads or to a slowly varying load or load change. For thispurpose the hydraulic drive for the resonance cylinder 11 has beenswitched off by means of the switching valve 15. Moreover, the controlor switching valve 19 has been actuated in such a manner that thecontrol ports 27, one of which is provided at each end of the secondcylinder 7, are now connected through respective hydraulic conduits 28to the source of hydraulic pres sure.

According to the invention, there is arranged a ring piston 29 on eachside of the piston 6 of the mean load cylinder 7. These ring pistons 29are slideable back and fourth along the respective portion of the pistonrod 6. These ring pistons 29 provide a seal relative to the inner wallof the cylinder 7. Such seal may be even improved by sealing rings 30 tobe described in more detail below.

In the so called resonance mode of operation, as described above, withreference to FIG. 1, the ring pistons 29 are located adjacent to therespective end of the cylinder 7 because the surfaces of the ringpistons 29 which face the piston 6 are subjected to the pressure mediumthrough the control port 18. However, if, as shown in FIG. 2,representing the slow drive mode of operation, the pressure medium isadmitted through the control openings 27 at the ends of the cylinder 7,the surfaces of the ring pistons 29 which face the respective end of thecylinder 7 are subjected to said pressure medium whereby these ringpistons 29 are pressed against the pistons 6. In this position the ringpistons 29 close the connecting ports 25 to the storage means 26 as wellas the control ports 18 which may also be referred to as inlet or outletcontrol ports.

The closing of the connecting ports 25 to the storage means 26 isnecessary during the so called slow drive mode of operation in order toavoid that the storage means 26 act as dead space.

In view of the foregoing, it will be appreciated that according to theinvention the switching over from one of the two possible modes ofoperation such as the resonance mode of operation or the slow drive modeof operation to the other mode of operation is accomplished simply byswitching the two control or switching valves and 19. The opening orclosing of the respective pressure medium ports in the cylinder 7,especially of the connecting port for the storage means 26 isaccomplished automatically by the shifting of the ring pistons 29 inresponse to the pressure medium. This constitutes a substantial advancein the art as compared to other devices for closing the respectivepressure medium ports for example, by means of valves or the likebecause the ring pistons 29 have the advantage that they may be producedrelatively easily. Besides, there are no special means required forkeeping the ring pistons 29 in their end positions. Another very substantial advantage is seen in that the ports to the storage means 26provide an unimpeded connection between the inner space of the cylinder7 and the respective storage means 26 which connection is free ofdisadvantageous throttling. Thus, the pressure drop between the storage26 and the cylinder 7 is rather small which has the important advantagethat a large resonance rise is possible during resonance operation.

Another advantage of the invention is seen in that during the so calledslow drive mode of operation large strokes of the piston 6 are possiblewithout any danger that the control ports 18 and the connecting ports 25are opened. This is so because, according to the invention, the controlports 27 which control said slow drive mode of operation are arranged atthe ends of the cylinder 7 and because the ring pistons 29 as may beseen from the diagrammatic showing of the drawings, may have asubstantial axial height. Moreover, for further facilitating the closingof the ports 18 and 25 during the slow drive mode of operation, theinvention provides the ring pistons 29 with sealing rings 30 which arearranged preferably at the outer ends of the ring pistons 29 that is,these sealing rings 30 are preferably arranged adjacent to the ringpiston end face which faces toward the respective end of the cylinder 7.This position of the sealing rings 30 at the outer ends of the ringpistons 29 has the further advantage that the ring pistons 29 will bepositively moved away from the piston 6 upon admission of pressuremedium through the ports 18 even if the ports 18, as may be seen in FIG.2, are not located in a plane defined by the contact between thesurfaces of the piston 6 and the ring pistons 29. It will be noted thatthe ports 18 are located slightly above and below the just-mentionedplanes.

The arrangement of the ports 18 and 25 approximately at the ends of thepoint of return of the piston 6, as mentioned above, is determined onlyby the length of the oscillating stroke during the resonance mode ofoperation in which situation the ring pistons 29 are located at theirrespective ends of the cylinder 7. in other words, when the ring pistons29 are in their end position remote from the piston 6, they must notclose the ports 18 and 25. The stroke performed by the piston 6 and thusby the ring pistons 29 during the slow drive mode of operation has noinfluence on the position of the ports 18 and 25 and, also as mentioned,the stroke during said slow drive mode of operation may be substantiallylarger than the oscillating stroke during the resonance mode ofoperation.

The pressure storage means 26 may be of conventional structure, forexample, these storage means may contain a compressable gas which isseparated from the pressure liquid by a membrane.

The central control unit 16 receives its input signals from the movementsensor 12 and also from the load cell 2. However, in addition, thecentral control unit may provide further control signals, for example,so called follow up signals which determine the load characteristic atthe hydraulic cylinder 7. Further, the central control unit 16 may havestored therein a complete program for controlling the testing system.

Although the invention has been described with reference to specificexample embodiments, especially example mode of operations, it is to beunderstood that it is intended to cover all modifications andequivalents within the scope of the appended claims.

What is claimed is:

1. A valving mechanism for hydraulic storage means, comprising a firsthydraulic piston cylinder arrangement including a first cylinder, afirst piston rod, a first piston rigidly secured to said first pistonrod for sliding in said first cylinder, and control ports in said firstcylinder on either side of said first piston, a second piston cylinderarrangement including a second cylinder, a second piston rod, a secondpiston rigidly secured to said second piston rod for slidingreciprocation in said second cylinder between return points, firstcontrol port means at each end of said second cylinder, second controlport means in said second cylinder intermediate its ends and aboutadjacent to said return points of reciprocation of said second piston,third port means in said second cylinder, hydraulic storage means,conduit means for connecting said hydraulic storage means to said thirdport means, ring piston means slideably located on said second pistonrod and on each side of said second piston whereby upon opening of saidfirst control port means the ring piston means are located adjacent tosaid second piston for closing said third ports to said hydraulicstorage means, whereas upon opening of said second control port meansthe ring piston means are located remote from said second piston meansfor opening said third ports, and means for interconnecting said firstand second piston rods.

2. The valving mechanism according to claim 1, wherein each of said ringpiston means comprises sealing means around its circumference forproviding a seal relative to said second cylinder.

3. The valving mechanism according to claim 2, wherein said sealingmeans are located adjacent to an end of the respective ring piston meanswhich end is remote from said second piston.

from said piston and closed when said ring piston means are locatedadjacent to said piston.

S. The valving mechanism according to claim 4, wherein each of said ringpiston means comprises sealing means around its circumference forproviding a seal relative to said cylinder.

6. The valving mechanism according to claim 5, wherein said sealingmeans are located adjacent to an end of the respective ring piston meanswhich end is remote from said piston.

1. A valving mechanism for hydraulic storage means, comprising a firsthydraulic piston cylinder arrangement including a first cylinder, afirst piston rod, a first piston rigidly secured to said first pistonrod for sliding in said first cylinder, and control ports in said firstcylinder on either side of said first piston, a second piston cylinderarrangement including a second cylinder, a second piston rod, a secondpiston rigidly secured to said second piston rod for slidingreciprocation in said second cylinder between return points, firstcontrol port means at each end of said second cylinder, second controlport means in said second cylinder intermediate its ends and aboutadjacent to said return points of reciprocation of said second piston,third port means in said second cylinder, hydraulic storage means,conduit means for connecting said hydraulic storage means to said thirdport mEans, ring piston means slideably located on said second pistonrod and on each side of said second piston whereby upon opening of saidfirst control port means the ring piston means are located adjacent tosaid second piston for closing said third ports to said hydraulicstorage means, whereas upon opening of said second control port meansthe ring piston means are located remote from said second piston meansfor opening said third ports, and means for interconnecting said firstand second piston rods.
 2. The valving mechanism according to claim 1,wherein each of said ring piston means comprises sealing means aroundits circumference for providing a seal relative to said second cylinder.3. The valving mechanism according to claim 2, wherein said sealingmeans are located adjacent to an end of the respective ring piston meanswhich end is remote from said second piston.
 4. A hydraulic valvingmechanism comprising a cylinder, a piston rod, a piston rigidly securedto said piston rod for slideable reciprocation in said cylinder, ringpiston means slideable on said piston rod on each side of said piston,first control ports at each end of said cylinder, second control portsintermediate the ends of said cylinder and about adjacent to points ofreturn of said piston reciprocation, and third ports also locatedsubstantially adjacent to said points of return of said pistonreciprocation whereby said third ports are opened when the ring pistonmeans are located remote from said piston and closed when said ringpiston means are located adjacent to said piston.
 5. The valvingmechanism according to claim 4, wherein each of said ring piston meanscomprises sealing means around its circumference for providing a sealrelative to said cylinder.
 6. The valving mechanism according to claim5, wherein said sealing means are located adjacent to an end of therespective ring piston means which end is remote from said piston.